What UI/UX Changes Were Made In iOS 7.1?

There are lots of small and some larger UI/UX changes in iOS 7.1. A decent overview is available here, or you can watch this video walkthrough of iOS 7.1 visual tweaks. Most notably (and excluding the entirely new feature CarPlay):

Animations are faster. The animations that accompany transitions —zooms when you open a folder or launch an app, slides when you move between pages, etc.— have all been accelerated, making the device feel snappier (related: performance on the iPhone 4 is improved significantly, a UX win for owners of the older model).

New UI for phone calls. The Phone app has some new UI elements which, along with the changes to the shut down screen, suggest that the "slide on a solid bar" element is being deprecated.

Button shapes and actionable-text underlining. You can now turn on "button shapes," which outline tappable areas roughly as the "button" shapes in iOS 6 did; this also underlines tappable text a la the web's hyperlinks. Note that this effect includes a rather strange dark coloring of buttons which are disabled or indicate canceling.

Toggle wallpaper effects without affecting zooming and transitions elsewhere. This is useful because many photos were hard to select as wallpapers due to unpredictable zoom effects; now those effects are optional, and can be seen when you choose the photo (not just after you do so and exit to the home or lock screen). This will allow more people to use both iOS 7's "ZUI" and animations / motions without having to sacrifice their preferred wallpaper.

Control the OS's white point and color brightness; and so on. Also, contrast has been improved in places like Control Center, where the light-grays and whites on a frosted nearly-white translucent background challenged the best of eyes when in direct sunlight. In the new Control Center, increased opacity makes everything much clearer, although against simpler backgrounds it's now hard to tell there's any translucency at all.

And there are many smaller improvements throughout the OS and
Apple apps like Calendar, iTunes Radio, and much more; the links above should provide a thorough accounting of them, but these seemed to me like the most notable.